I always thought that the "rule" referred to is that "all rules have exceptions" (R1). i.e. there's a rule (in this case "only men with big beards can tame a unix system" (R2)) which, however, has an exception ("girls in dinosaur themeparks can also do so" (E1)). Therefore, the R1 is, once again, shown to be true.

Hmmm... self-referential vibes coming here. It might be that the only exception to the R1 is itself, but then... etc.